The classification method the device uses for processing banknotes is described in international application WO 2007/068867 (published on Jun. 21, 2007, IPC G07D7/20). The device scans a banknote and obtains its digital scan consisting of the banknote two-dimensional images. The device is equipped with a computing unit for a computational processing of the digital scan.
In compliance with the above-mentioned method, an automatic validation uses a set of classifiers of the same class; each classifier is applied to a set of average values of the individual areas of the image. The image areas to be averaged are defined according to partitioning scheme specified individually for each classifier. The classifier of one class is a computational process whose result is an estimating statistical characteristic. Each known class has a criterion of banknote membership in a specific class; the criterion is based on making comparison of the value of the estimating statistical value for the given class with a predefined threshold value. In compliance with this method, classifiers for all known classes are successively applied to the banknote scan, and only then their results are analyzed, and a conclusion is drawn that the banknote belongs to some class.
One of the drawbacks of the method described in the above-mentioned application is an individual area partitioning scheme used for each classifier. It means that average values for the areas shall be calculated separately for each classifier. Another shortcoming of the given method is that the main computational processing (calculation of average values and calculation of classifiers) for each possible class is carried out in the same volume, and only then the result is analyzed. Both imperfections result in a serious computational complexity, especially when the number of classifiers in use is large. Serious computational complexity in turn demands a high performance computing unit.
This method is characterized by a practically linear increase in the performance requirements for the device computing unit if the number of classes the banknote may belong to rises. It is due to an independent checking of the banknote correspondence to each possible class. So, it is extremely difficult for implementation of the known method to develop a device that may work with a considerable number of currencies of various countries.